Heat exchanger for compressed air dryer

ABSTRACT

A heat exchanger for removing moisture from compressed air and other gases in which the precooling, cooling and reheating sections are in telescoped relation.

United States Patent [191 Freese Primary ExaminerWilliam J. WyeAttorney, Agent, or FirmRalph Hammar [57] ABSTRACT A heat exchanger forremoving moisture from compressed air and other gases in which theprecooling, cooling and reheating sections are in telescoped relation.

16 Claims, 3 Drawing Figures HEAT EXCHANGER FOR COMPRESSED AIR DRYER[76] Inventor: Charles E. Freese, 5140 Woodland,

Forest Park, Ga. 30050 [22] Filed: Apr. 26, 1973 [21] Appl. No.: 354,890

[52] US. Cl. 62/272, 62/90, 62/92, 62/93, 62/317, 62/428 [51] Int. Cl.F25d 21/00 [58] Field of Search 62/90, 93, 92, 428, 272, 62/317 [56]References Cited UNITED STATES PATENTS l,093,869 4/1914 Leinert 62/93 ln 9 a A 1- a A |O-i A 30- A z= A 15- A a, i-E 4 n si PATENTED JUN25 19741 HEAT EXCHANGER FOR COMPRESSED DRYER This invention is intended toincrease the efficiency and reduce the cost of manufacture and operationof heat exchangers for removing moisture from air or other gases. In apreferred form, the heat exchanger is shown for removing moisture fromcompressed air but other uses are obviously possible.

In the drawing, FIG. 1 is a section through a heat exchanger forremoving moisture from compressed air and the like, FIG. 2 is a sectionon line 2-2 of FIG. I, and FIG. 3 is a section through anotherembodiment.

In FIG. I there is shown a tank having side walls I and upper and lowerheaders 2, 3. At the lower end of the side walls are inlet and outletfittings 4, 5 for connection in a compressed air line. The tank and itsfittings are constructed to withstand the air pressure. The tank isshown as of circular cross section but obviously other shapes could beused. Within the tank are heat exchange passageways 6, 7, 8, 9 intelescoping relation to each other. The heat exchange passageway 6,which is outermost, is formed by a wall 10 spaced inward from the innersurface of the wall 1 and extending between an annular lower header 11and an annular upper header 12. The lower header II is fixed to the sidewall I of the tank below the inlet fitting 4 and supports the wall 10and also closes the lower end of the passageway 6 so that the incomingair is directed upward in the direction of arrow 13. The header l2 atthe upper end of the wall 10 directs the flow from the outlet ofpassageway 6 in the direction of arrow 14 to the inlet end of passageway9 formed between a wall 15 depending from the header l2 and a conduit 16for a refrigerant. The refrigerant enters the lower end of conduit 16 asindicated by arrow 17 and flows out the upper end as indicated by arrow18. The outer surface of the conduit 16 may be provided with spikes orfins 19 or other expedients for increasing the heat exchange surface.Expedients for increasing the heat exchange surface may obviously beused for the other walls forming heat exchange passageways. Whileflowing through the passageway 9, the air temperature is lowered belowits dew point and moisture and other condensibles are condensed, fallinginto a sump 20 formed by the header 3. Dirt entrained in the air alsofalls into the sump. A drain fitting 21 is provided to remove excessiveliquid accumulation in the sump. Some liquid in the sump is advantageoussince this liquid is cooled by the refrigerant in conduit 16 andtherefore provides a further heat exchange surface for lowering the dewpoint of the air and thereby removing moisture. The enlarged space 22between the outlet 23 of passageway 9 and the inlet 24 of passageway 8encourages moisture drop out and discourages entrainment of moisture inthe air entering the inlet of passageway 8.

The air entering the lower end of passageway 8 flows upward as indicatedby arrow 25 and at its upper or outlet end 26 is deflected downward byheader 12 into the inlet end 27 of passageway 7 as indicated by arrow28. Passageway 7 is in heat exchange relation to wall 10 of passageway 6and also to wall 29 of passageway 8. The heat exchange relation to wall10 serves to precool the incoming air flowing in the direction of arrow,13. The heat exchange relation to the wall 29 is minimized by makingwall 29 of a poor heat conductor. While the inlet air flowing in thedirection of arrow 13 is being precooled, the air flowing downwardthrough passageway 7 in the directionof arrow 30 is being reheated. Atthe lower or outlet end of passageway 7 the header l1 deflects the airto the outlet fitting 5.

The walls 10, 15, 29 which form the heat exchanging passageways are allsupported by the header 11. These walls may be of thin metal since noneof these walls is required to stand the operating pressure of the air.Both headers 11 and 12 also have the function of directing the air flowthrough the heat exchanger passageways, as described above. Thestructure has high thermal efficiency because the warm incoming air isat the outside of the tank and the cold or dehydrated air is at thecenter of the tank. Sharing of walls of the heat exchanger passagewaysimproves the thermal efficiency by direct conduction of heat from theair through the metal walls. Wall 15 is shared by passageways 8, 9. Wall29 is shared by passageways 7, 8. Wall 10 is shared by passageways 6, 7.The structure also makes efficient use of space due to the sinuous airflow of the heat exchanging surfaces. The structure further simplifiesthe construction and reduces the space requirements.

In FIG. 3 there is shown a modification in which the dew point of theair is lowered by chilled liquid spray and in which the inlet and outletfor the compressed air is at the top of the tank rather than at thebottom. Obviously the cooling apparatus of FIG. 3 could be substitutedin FIG. 1 and vice versa.

In the structure of FIG. 3, the tank has upper and lower headers 41, 42and inlet and outlet fittings 43, 44 for compressed air. These parts aresized to withstand the air pressure. Within the tank are heat exchangepassageways 45, 46, 47, 48 in telescoping relation to each other. Thepassageway is formed by a wall 49 and the inner surface of side wall 40of the tank. The wall 49 is fixed at its upper end and supported by theheader 41 and at its lower end is fixed to an annular header 50extending between wall 49 and a wall 51 which defines the passageway 48.The compressed air entering inlet 43 is compelled to flow downwardthrough the passageway 45 and enters the lower end of passageway 48 andflows upward as indicated by arrow 52. While flowing up throughpassageway 48, the air is cooled by a refrigerated liquid spray obtainedfrom a liquid chiller 53 and circulated by a pump 54 from a sump 55 inheader 42 to a spray head 56 discharging into the upper end ofpassageway 48. A series of staggered baffles 57 provide an extended gasand liquid contact interface between the compressed air and the chilledliquid. This results in cooling of the compressed air below its dewpoint so that the moisture is absorbed by the liquid which falls intothe sump as indicated by drops 58. The liquid in the sump provides afurther heat exchange surface for cooling the air entering the lower endof passageway 48. Excess accumulation of liquid in the sump is preventedby a valve 59. If the liquid is chilled below the freezing point of themoisture, an anti-freeze is required. This is obtained from an injector60 having a sensing element 61 responding to the freezing temperature ofthe liquid in the sump which injects anti-freeze through line 62 asrequired by the sensor. When the injector is used, the outlet from thecontrol valve 59 would ordinarily lead to anti-freeze recovery apparatussuch as a still.

The cooled air leaving the upper or outlet end of the passageway 48flows downward through passageway 47 formed by wall 51 and a surroundingwall 63 which is supported by the header 41. Air leaving the lower oroutlet end of passageway 47 flows upward into the inlet end ofpassageway 46 formed between the walls 49 and 63. At the outlet end ofthe passageway 46 the air is deflected by the header 41 into the outletfitting 44.

In the operation, the incoming compressed air from inlet fitting 43 isprecooled by the air in passageway 46. This heat exchange both precoolsthe incoming air and reheats the outgoing air leaving fitting 44. Theair is further cooled by contact with the liquid in the sump 55 and bythe liquid spray in passage 48.

In both forms of the invention, the heat exchange passageways are intelescoping relation, improving the thermal efficiency and decreasingthe space requirements and the cost of production. Only the tanks andits headers are sized to withstand the operating pressure. The internalwalls are designed for heat transfer and not forpressure.

What is claimed is:

1. Apparatus for dehumidifying air or other gas comprising a pluralityof telescoped passageways each having an inlet at one end and an outletat the opposite end, a first passageway being outermost with its inletreceiving air to be dehumidified, a second passageway being innermostwith its inlet receiving the air from the outlet of the first passagewayand conducting such air in the opposite direction to the direction offlow in the first passageway and having therein refrigerating means inheat exchange relation to such air, a third passageway surrounding andin heat exchange relation to the second passageway with its inletreceiving the air from the outlet of the second passageway andconducting such air in the same direction as the direction of flow inthe first passageway, and a fourth passageway between and in heatexchange relation to the first passageway with its inlet receiving theair from the outlet of the third passageway and conducting such air inthe opposite direction to the direction of flow in the first passageway,the flow being sequentially through the first, second, third and fourthpassageways.

2. The apparatus of claim 1 in which the third passageway shares a wallwith the second passageway and also shares a wall with the fourthpassageway.

3. The apparatus of claim 1 in which the fourth passageway shares a wallwith the first passageway.

4. The apparatus of claim 1 having a tank with inlet and outletfittings, the first passageway being connected to the inlet fitting andformed between the inner surface of a side wall of the tank and a firstwall spaced inward from said surface and the fourth passageway beingconnected to the outlet fitting and formed between said first wall and asecond wall spaced inward from said first wall.

5. The apparatus of claim 4 in which a third wall forms the secondpassageway and is spaced inward from the second wall to form the thirdpassageway.

6. The apparatus of claim 5 in which the tank has upper and lowerheaders and the lower header provides a sump below said second and thirdwalls.

7. The apparatus of claim 6 in which the sump is refrigerated to providea further cooling surface.

8. The apparatus of claim 1 in which the refrigerating means comprises achilled liquid spray.

9. The apparatus of claim 1 in which the refrigerating means comprises aconduit carrying in said second passageway a refrigerating medium.

10. The apparatus of claim 8 in which the chilled liquid is a solutionwith a freezing point below the normal freezing point of water.

11. The apparatus of claim 4 in which the first and second walls aresupported by a header fixed to the tank.

12. The apparatus of claim 5 in which the third wall is supported bysaid header.

13. The apparatus of claim 5 in which the tank has upper and lowerheaders and the lower header provides a sump below said third wall.

14. The apparatus of claim 5 in which the tank has upper and lowerheaders and the lower header provides a sump below said first, secondand third walls.

15. The apparatus of claim 13 in which the sump is refrigerated toprovide a further cooling surface.

16. The apparatus of claim 14 in which the sump is refrigerated toprovide a further cooling surface.

1. Apparatus for dehumidifying air or other gas comprising a pluralityof telescoped passageways each having an inlet at one end and an outletat the opposite end, a first passageway being outermost with its inletreceiving air to be dehumidified, a second passageway being innermostwith its inlet receiving the air from the outlet of the first passagewayand conducting such air in the opposite direction to the direction offlow in the first passageway and having therein refrigerating means inheat exchange relation to such air, a third passageway surrounding andin heat exchange relation to the second passageway with its inletreceiving the air from the outlet of the second passageway andconducting such air in the same direction as the direction of flow inthe first passageway, and a fourth passageway between and in heatexchange relation to the first passageway with its inlet receiving theair from the outlet of the third passageway and conducting such air inthe opposite direction to the direction of flow in the first passageway,the flow being sequentially through the first, second, third and fourthpassageways.
 2. The apparatus of claim 1 in which the third passagewayshares a wall with the second passageway and also shares a wall with thefourth passageway.
 3. The apparatus of claim 1 in which the fourthpassageway shares a wall with the first passageway.
 4. The apparatus ofclaim 1 having a tank with inlet and outlet fittings, the firstpassageway being connected to the inlet fitting and formed between theinner surface of a side wall of the tank and a first wall spaced inwardfrom said surface and the fourth passageway being connected to theoutlet fitting and formed between said first wall and a second wallspaced inward from said first wall.
 5. The apparatus of claim 4 in whicha third wall forms the second passageway and is spaced inward from thesecond wall to form the third passageway.
 6. The apparatus of claim 5 inwhich the tank has upper and lower headers and the lower header providesa sump below said second and third walls.
 7. The apparatus of claim 6 inwhich the sump is refrigerated to provide a further cooling surface. 8.The apparatus of claim 1 in which the refrigerating means comprises achilled liquid spray.
 9. The apparatus of claim 1 in which therefrigerating means comprises a conduit carrying in said secondpassageway a refrigerating medium.
 10. The apparatus of claim 8 in whichthe chilled liquid is a solution with a freezing point below the normalfreezing point of water.
 11. The apparatus of claim 4 in which the firstand second walls are supported by a header fixed to the tank.
 12. Theapparatus of claim 5 in which the third wall is supported by saidheader.
 13. The apparatus of claim 5 in which the tank has upper andlower headers and the lower header provides a sump below said thirdwall.
 14. The apparatus of claim 5 in which the tank has upper and lowerheaders and the lower header provides a sump below said first, secondand third walls.
 15. The apparatus of claim 13 in which the sump isrefrigerated to provide a further cooling surface.
 16. The apparatus ofclaim 14 in which the sump is refrigerated to provide a further coolingsurface.